End-to-end joints of pipes made of metal material may be implemented in many different ways. One example of previously known solutions is a joint structure, in which a fastening collar is formed to a pipe end in a device with a rotating shaping cone, for instance. The fastening collar is formed in such a manner that the collar is at a substantially 37-degree angle to the longitudinal axis of the pipe. An inner piece is connected to the flange formed in the above-mentioned manner to provide sealing. The structure also has a tightening flange and tightening elements, with which the structure is tightened against a second corresponding structure. Such a structure is described in FI patent publication 70080.
A drawback of the structure described above is the high cost of manufacture. The high cost is caused, in particular, by the manufacture of the inner piece that requires precision work and increases costs substantially. The drawback is especially emphasized in connection with large-diameter pipes.
Another example of solutions known in the field is a solution, in which the fastening collar is formed in two steps. In the first step, the fastening collar is shaped to be at a substantially 37-degree angle to the longitudinal axis of the pipe. In the second step, the fastening collar is shaped to be at a 90-degree angle to the longitudinal axis of the pipe. This type of solution is shown in FI Patent 89137.
A drawback in the structure described above is the shaping of the fastening collar to the 90-degree angle, which is a difficult step in terms of the pipe material, since material elongation, or degree of deformation, at the bend is relatively large in this type of shaping.